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```95 8                            Appendix IV.

A B is the fixed link, B P the driver travelling uniformly say, and A c

is the driven link having a varying angular velocity.    Following the                    '•

method of p. 493, and considering B as the diagram centre, B P =

velocity of driver at any point, and D E F K is a polar curve shewing

o> of driver.    Also GHFJ is a polar curve shewing w of AC by its

Proceeding, let BP== linear velocity of P, and complete the parallelo-
gram LPMB. Then with centre B, turn L round to N, and M to Q.
Doing this for various positions, we have constructed the polar curve
D Q F S, shewing linear velocity of slider P normal to A C. Similarly
the polar curve B N T shews linear velocity of slider P sliding along AC.
For proof, PRV is a triangle of velocities, drawn (i) right angles to

,                           P B, (2) right angles to A c, (3) parallel to A C, and it is easily seen that                    *

triangle B P L is similar.                                                                                        f

j                          P. 553.  Electric Accumulators or Secondary Bat-

ij                         teries.,—The PlantŁ and Faure cells have already been generally

I                         described.   Both kinds of cells are still used, the E.P.S. being a

J                         Faure cell, and the Epstein a PlantŁ cell, while the Chloride Co.

'I                         claim to unite the advantages of both types.    In the Faure cell

'i                         the plates are lead grids, whose holes are filled with paste made

"l                             as follows:—                                                    *

'I                              Positive plate: red lead (Pb8O4) mixed with dilute sulphuric

|                                   acid.                   .                   .

I                              Negative plate: litharge (PbO)- mixed with dilute sulphuric

1                      •            acid.                           . •   ""       .'       •   •

)                              (Note : Comparing with a primary battery, the + is equivalent

%                         to zinc and the — to copper)

]                              The probable condition in the Plante* battery is :

-h Plate     Electrolyte      - Plate

When charging     ...    PbO2  -h 2 H2SO4 + PbO.

When discharging...    PbS04+  2 H2O   + *PbSO4.

While in the Faure cell the reaction may be:

>                          -f Plate,    charging : PbS04 + 2 H2O + S(\ * PbO^-f- 2 H2SO4

-Plate,    charging: PbSO^  H2              = Pb     + H2S04

+ Plate, discharging: Pb02 + 2 H2SO4 + H2= PbSO4+ 2 H2O
- Plate, discharging: Pb      + SO                = PbSO

Fig. 897 shews diagrammatically the ari»ngement of the plates
la a two-cell "battery. The electrolyte or conducting liquid```